The vtable that you are printing is not a vtable (MONO_TYPE_END is 0). You can
see that in major_copy_or_mark_object_with_evacuation ptr and obj are equal
which doesn’t make any sense. Looks like something corrupted the static_data
that the gc scans. Maybe some bug around mono_alloc_special_static_data or the
gc suspended the thread somewhere in an intermediate state.
Vlad
From: Mono-devel-list <mono-devel-list-boun...@lists.dot.net> on behalf of
Neale Ferguson <ne...@sinenomine.net>
Date: Wednesday, 16 August 2017 at 23:19
To: Mono-Devel <mono-devel-l...@lists.ximian.com>
Subject: [Mono-dev] sgen debugging
Apologies for the last email. I thought I'd fixed that problem but Outlook
continues to screw me. Using a different client now -
Running a test in mono/tests I get the following:
#0 0x00000000802b7dc0 in par_copy_object_no_checks (objsize=0, obj=0x804ed290,
vt=0x804ed290,
destination=0x3fffab5c130 "") at sgen-copy-object.h:53
#1 copy_object_no_checks (obj=obj@entry=0x804ed290,
queue=queue@entry=0x3ffffffec48) at sgen-copy-object.h:80
#2 0x00000000802c31cc in major_copy_or_mark_object_with_evacuation
(queue=0x3ffffffec48, obj=0x804ed290,
ptr=0x804ed290) at sgen-marksweep-drain-gray-stack.h:84
#3 major_copy_or_mark_object_canonical (ptr=0x804ed290, queue=0x3ffffffec48)
at sgen-marksweep.c:1358
#4 0x00000000802212c0 in mark_slots (addr=0x804ed290, bitmaps=0x8044c600
<thread_reference_bitmaps>,
mark_func=0x802a42dc <single_arg_user_copy_or_mark>, gc_data=0x3ffffffe7a8)
at threads.c:4013
#5 0x00000000802a4eae in precisely_scan_objects_from (ctx=..., desc=<optimized
out>, end_root=0x804ed690,
start_root=0x804ed290, n_start=<optimized out>, n_end=<optimized out>) at
sgen-gc.c:935
#6 scan_from_registered_roots (ctx=..., root_type=<optimized out>,
addr_start=<optimized out>,
addr_end=<optimized out>) at sgen-gc.c:1256
#7 job_scan_from_registered_roots (worker_data_untyped=<optimized out>,
job=<optimized out>) at sgen-gc.c:1400
#8 0x00000000802e83c0 in sgen_workers_enqueue_job (generation=<optimized out>,
job=0x3fffd07f008,
enqueue=<optimized out>) at sgen-workers.c:181
#9 0x00000000802a4386 in enqueue_scan_from_roots_jobs
(gc_thread_gray_queue=0x3ffffffec48, heap_start=0x0,
heap_end=0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>,
ops=0x8049d558 <major_collectorﮞ>, enqueue=0) at sgen-gc.c:1640
Gdb shows the SEGV here:
Program received signal SIGSEGV, Segmentation fault.
0x00000000802b7dc0 in par_copy_object_no_checks (objsize=0, obj=0x804ed290,
vt=0x804ed290,
destination=0x3fffab5c130 "") at sgen-copy-object.h:53
53
memcpy ((char*)destination sizeof (mword), (char*)obj sizeof (mword), objsize -
sizeof (mword));
(gdb) up
#1 copy_object_no_checks (obj=obj@entry=0x804ed290,
queue=queue@entry=0x3ffffffec48) at sgen-copy-object.h:80
80
par_copy_object_no_checks ((char *)destination, vt, obj, objsize);
(gdb) list 65
65
static MONO_NEVER_INLINE GCObject *
66
copy_object_no_checks (GCObject *obj, SgenGrayQueue *queue)
67
{
68
GCVTable vt = SGEN_LOAD_VTABLE_UNCHECKED (obj);
69
gboolean has_references = SGEN_VTABLE_HAS_REFERENCES (vt);
70
mword objsize = SGEN_ALIGN_UP (sgen_client_par_object_get_size (vt, obj));
71
void *destination = COLLECTOR_SERIAL_ALLOC_FOR_PROMOTION (vt, obj, objsize,
has_references);
72
73
if (G_UNLIKELY (!destination)) {
74
/* FIXME: Is this path ever tested? */
(gdb) p vt
$5 = (MonoVTable *) 0x804ed290
(gdb) p obj
$6 = (GCObject *) 0x804ed290
(gdb) p *vt
$7 = {klass = 0x804ed290, gc_descr = 0, domain = 0x0, type = 0x0,
interface_bitmap = 0x0, max_interface_id = 0,
rank = 0 '\000', initialized = 0 '\000', remote = 0, init_failed = 0,
has_static_fields = 0, gc_bits = 0,
imt_collisions_bitmap = 0, runtime_generic_context = 0x0, vtable = 0x804ed2d0}
(gdb) p *vt->klass
$8 = {element_class = 0x804ed290, cast_class = 0x0, supertypes = 0x0, idepth =
0, rank = 0 '\000',
instance_size = 0, inited = 0, size_inited = 0, valuetype = 0, enumtype = 0,
blittable = 0, unicode = 0,
wastypebuilder = 0, is_array_special_interface = 0, min_align = 0 '\000',
packing_size = 0, ghcimpl = 0,
has_finalize = 0, marshalbyref = 0, contextbound = 0, delegate = 0,
gc_descr_inited = 0, has_cctor = 0,
has_references = 0, has_static_refs = 0, no_special_static_fields = 0,
is_com_object = 0,
nested_classes_inited = 0, class_kind = 0, interfaces_inited = 0, simd_type =
0, has_finalize_inited = 0,
fields_inited = 0, has_failure = 0, parent = 0x0, nested_in = 0x0, image =
0x0, name = 0x0, name_space = 0x0,
type_token = 0, vtable_size = 0, interface_count = 0, interface_id = 0,
max_interface_id = 0,
interface_offsets_count = 0, interfaces_packed = 0x0,
interface_offsets_packed = 0x0,
interface_bitmap = 0x3fffafd8130 "", interfaces = 0x0, sizes = {class_size =
1023, element_size = 1023,
generic_param_token = 1023}, fields = 0x0, methods = 0x3fffafd8270,
this_arg = {data = {klass = 0x0,
type = 0x0, array = 0x0, method = 0x0, generic_param = 0x0, generic_class
= 0x0}, attrs = 0,
type = MONO_TYPE_END, num_mods = 0, byref = 0, pinned = 0, modifiers =
0x804ed33c}, byval_arg = {data = {
klass = 0x0, type = 0x0, array = 0x0, method = 0x0, generic_param = 0x0,
generic_class = 0x0}, attrs = 0,
type = MONO_TYPE_END, num_mods = 0, byref = 0, pinned = 0, modifiers =
0x804ed34c}, gc_descr = 0,
runtime_info = 0x0, vtable = 0x0, infrequent_data = {head = 0x0}}
I am wondering what MONO_TYPE_END is and whether it should be looked at by gc
or what might have happened to get me to this point?
Neale
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